Rats See Double: Rodent Eyes Adapted to Watch Predators

Rats may have more advanced vision than we once thought. Researchers have discovered that rats move their eyes in opposite directions in both the horizontal and vertical plane when running around. That's one way to keep an eye on predators.

Like many mammals, rats have their eyes on the sides of their heads. This gives them a very wide visual field, which is useful for detecting predators. However, three-dimensional vision requires overlap of the visual fields of the two eyes. This means that the visual system needs to meet two conflicting demands at the same time: maximum surveillance and detailed, binocular vision.

In order to examine the minute eye movements of rates, researchers watched the rodents with miniaturized high-speed cameras and high-speed behavioral tracking. The fitted cameras weighed only about one gram and were placed on the animals' heads. After observing the rats' eye movements, the researchers were able to figure out what they were probably seeing.

The scientists discovered that rat eyes work in a completely different way. Eye movements depend largely on the position of the animal's head. In addition, they discovered that rats didn't fuse visual information into a single image like humans do. Instead, rats see in such a way that the space above them is permanently in view.

"Humans move their eyes in a very stereotypical way for both counteracting head movements and searching around," said Jason Kerr from the Max Planck Institute for Biological Cybernetics in a news release. "Both our eyes move together and always follow the same object. In rats, on the other hand, the eyes generally move in opposite directions."

In fact, eye movements in rats vary by as much as 40 degrees in the horizontal plane and up to 60 degrees in the vertical plane. This means that the area above the animal is always in view, despite head movements in all planes. This particular attribute is extremely useful when avoiding predators in the air, such as owls or hawks.

So how do rats see? It turns out they're highly adapted to evade predators. The findings reveal a little bit more about these creatures and could allow scientists to better understand and study vision in the future.

The findings are published in the journal Nature.